The seal attack on Saturday marked the fourth time a shark has been spotted at Nauset Beach, leading to the closure.
"We saw some more splashing of water, and then the blood started spreading out more," said a witness.
A fellow passenger captured the incredible moment the shark leaped at their boat.
Police are investigating the legs, but aren't yet sure if any laws have been broken.
The video was captured by a team of researchers from the non-profit Atlantic White Shark Conservancy.
The man denied the charge of open and gross lewdness.
"It doesn't feel like I did anything heroic," the survivor said. "A lot of this was luck."